How Do Venus Flytraps Work?

Venus flytraps can photosynthesize like most other plants, but they supplement their diet by catching insects and arachnids. Learn what we know (and don't know!) about how they accomplish this feat in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/life/botany/venus-flytrap.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuf, a production of iHeartRadio, Hey brain Stuff
Lauren volebamb Here. Plants that eat animals may sound like
the premis for a horror story, but there's nothing supernatural
about it. Carnivorous plants have existed on this planet for
millions of years. There are more than five hundred different

(00:23):
kinds with appetites, ranging from single celled organisms to insects
to spiders. Today, let's talk about one of the most famous,
the venus flytrap. The venus flytrap grows roots, stems, leaves, flowers,
and seeds just like most plants, but it also grows
two specialized lobes on the end of each leaf that

(00:45):
form a hinged trap. Those lobes are distinctively green on
the outside and reddish pink on the inside, with small
bristles along the edges. But when they're open, they look
like toothy little mouths calling for a snap. And when
an insect or a racknid crawls across that pinkish inner surface,
the trap slams shut and the plant digests its prey.

(01:09):
It's a mouth and stomach in one. Although the venus
flytrap has captivated people across the world. Wild populations of
these plants actually grow in an incredibly small geographic area,
a region along the coasts of North and South Carolina,
only some seventy five square miles in area, that's about
two hundred square kilometers. Their native areas are bogs and

(01:31):
wetlands that are humid and sunny. They're so scarce that
some early botanists doubted their existence despite all the stories
spread about a flesh eating plant. But okay, if other
plants can thrive on nothing but water, air, nutrients in
the soil, and some sunshine, why do venus flytraps eat insects?

(01:54):
Flytraps actually get a good deal of their sustenance just
like other plants do. During photosynthesis, plants use the energy
of the sun to drive a reaction that converts carbon
dioxide and water into sugar and oxygen. The sugar produced
is then converted to energy that the plant cells can
use a molecule called adenosine triphosphate or ATP. ATP is

(02:15):
what our cells used to get stuff done too. However,
in addition to sugar, plants also need to make amino acids, vitamins,
and other cellular components to survive in the coastal bogs
where venus flytraps live, the soil is acidic and minerals
and other nutrients are scarce. Most plants can't survive in
this environment because they can't make enough of the building

(02:37):
blocks necessary for growth. The venus flytrap evolved an alternate
means of getting those key nutrients. Living creatures like insects
provide a good source of the stuff that's missing from
the soil, plus additional carbohydrates so that covers the y.
But how do these plants catch and eat prey. A
plant doesn't have a brain or even a nervous system

(03:00):
to coordinate their functions and movements, nor do they have bones, tendons,
and muscles to coordinate. But most plants do have some
way of attracting animals or insects, regardless of whether they're
going to eat them. Lots of flowering plants have evolved colors, scents,
and sugary nectar to attract bees, butterflies, and other pollinators.

(03:22):
In those cases, the animals get a snack, and they
unwittingly ferry the plant's pollen to neighbors of the same species,
thus fertilizing them. Hopefully. Similarly, fruits evolved to be sweet
and tasty because if a bird or other animal eats
them and later poops the seeds elsewhere unharmed, a new
plant can grow. In the case of the venus flytrap,

(03:45):
the inner surface of those specialized lobes secretes a sweet
nectar that draws in insects searching for food. But the
inner surfaces of the lobes also sport short, stiff, hair
like structures that serve as a sort of motion to
When a creepy crawley crawls across the surface and brushes
two hairs in close succession or one twice, the lobes

(04:09):
close down in as little as half a second, trapping
the creature inside a fun fact or black thereof No
one knows exactly how this works, ever since Charles Darwin
described the species in eighteen seventy five, and he called
it the most wonderful plant by the way. Ever since then,
researchers have been trying to get to the bottom of

(04:31):
this trapping mechanism, but it's difficult to observe what's going
on inside a living plant during half a second of action.
The prevailing hypothesis goes that a venus fly trap accomplishes
this feat by rapidly changing the geometry of those specialized
lobes via water transfer within the lobes upon stimulus. Let

(04:52):
me break that down, Okay. Each lobe or half of
a venus flytrap's trap seems to have two functional layers inside,
an upper layer up against the pinkish interior surface of
the trap and a lower layer up against the green
outer surface of the trap. Cells within the layers contain water.

(05:13):
That's not unusual. Cells generally do contain water, but the
upper and lower layers are each capable of holding onto
water and of transferring it quickly to each other. When
the trap is open. That's actually a tense state for
the lobes of the leaf, wherein more water is being
held by the upper interior layer of cells. This makes

(05:37):
each lobes slightly convex and holds the trap open. But
when something triggers those motion detector hairs that somehow tells
the plant to open up pores between the upper and
lower layers, water quickly moves into the lower outer layer,
making each lobes lightly concave, curling in around its prey.

(05:59):
In a fraction of a second, this closed state is
relaxed for the lobes of the leaf. They open back
up again by slowly transferring water back to the upper
interior layer, but it takes a while. Again, no one
entirely understands how all this works, though there is some
interesting research into all the biochemical details. But for our

(06:22):
purposes today, let's focus in on what happens when that
trap does close on some tasty prey. The lobes of
the leaf form an airtight seal so that digestive fluids
and insect parts are kept inside the trap, and so
that bacteria and molds can't get in. Those toothy looking
spines on the outer edges of the trap laced together

(06:45):
and latch the trap shut. There is an upper limit
to the size of insect that a trap can accommodate.
The traps will grow up to around an inch long
or about two and a half centimeters, and in order
to close tightly, an insect that catches can only be
about a third of that size. If an insect is
too large, the trap can't form a seal against microbes,

(07:05):
which will move in and eat the decomposing insect and
the trap itself too. The trap will turn black and
drop off of the plant, but back to dinner. Once
an insect or a rapnet is firmly ensconced in the trap,
the process of digestion can begin. The trap now serves
as a miniature stomach, just like our stomachs. The trap

(07:28):
secrete acidic digestive juices that do three things. They dissolve
the soft tissues and sell membranes of the food. They
serve as an antiseptic to kill any microbes that got
in with the food, and they break down various proteins
and other molecules into small pieces that the plant can
take in. It takes some five to twelve days for

(07:48):
a trapped digest prey, depending on the size of the prey,
the age of the trap, and the ambient temperature. Older
traps and colder temperatures make digestions slower. The process continues
until all that's left of the insect is its herd
exoskeleton and its bath of digestive juices. The plant reabsorbs
the fluids and the trap slowly reopens, after which the

(08:12):
praise remains are usually either washed away in the rain
or blown away by the wind. A venus fly trap
can tell the difference between living prey and a dead
exoskeleton or other non edible debris that might fall in.
Inanimate objects that trigger the trap's motion sensitive hairs won't
keep moving once it slams shut. If there's no further

(08:32):
stimulation of the hairs, the trap won't seal up, but
it will be stuck in partially shut state until tension
can be re established in the lobes of the trap.
This process takes about twelve hours, at which point the
unwonted object falls out. This selection process is pretty good,
but not perfect. While the trap is out of commission,

(08:53):
real food may be crawling all around the plant. Imagine
if you had to sit with a chicken bone or
peach pit in your mouth for twelve hours while the
rest of your dinner sat on the table in front
of you. Of course, the venus fly trap doesn't feel
any kind of way about it. It's a passive participant
in the process of eating dinner. Any given trap won't

(09:13):
last the full lifetime of the plant. After about ten
to twelve closures, either partial or complete, the trap will
stop trapping and remain partially open. It'll devote its remaining
time to photosynthesis, usually for around two to three months,
while our imaginations dream up people eating killer plants. In reality,

(09:36):
we're the threat to venus fly traps and other carnivorous
plants in the wild. Venus fly traps today only cover
about a third of their historic range. In the nineteen seventies,
there were around four million of them. That's down to
just over three hundred thousand as of twenty twenty due
to over collection by humans and the draining and destruction
of the natural wetlands where they grow. There's a hefty

(09:59):
fine North Carolina felony charge for removing them from the wild,
but lots of reputable plant nurseres propagate and sell them legally.
If you grow one at home, you'll be looking to
replicate its boggy, bright homeland with specialized soil and humid conditions.
A terrarium can help. Check growing guides online or talk

(10:19):
to your local garden center. A venus flytrap will grow
to about five inches or thirteen centimeters tall, with about
four to eight traps per plant. You'll want to provide
it with two or three small flying insects like a
house fly every month. A far cry from the feed
me seemore eating habits of carnivorous plants in science fiction.

(10:44):
Today's episode is based on the article how Venus flytraps
work on HowStuffWorks dot Com, written by Anne Mieker O'Connell.
Brain Stuff is production of iHeartRadio in partnership with HowStuffWorks
dot Com and is produced by Tyler Klain. Four more
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